Fibrous solid propellants in sheet form



July 4, 1961 e. NADEL 2,991,168

FIBROUSSOLID PROPELLANTS IN SHEET FORM Filed Nov. 18, 1957 Fiber 1149b 79/7771); 8 flona l ng 5 open er a arazus age} if ICE 10/2 lsicfclra B Natl EL BY m: gimu T jwwa 6070M 2,991,168 FIBROUS SOLID PROPELLANTS IN SHEET FORM I Isidore G. Nadel, 55D Braun Place, Clifton, NJ. Filed Nov. 18, 1957, Ser. No. 697,297 5 Claims. (Cl. 52-5) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to highly combustible fibrous sheet material. More particularly the invention concerns nonwoven fabrics, webs, papers and the like composed at least in part of solid propellant compositions in textile-type filamentary form.

Numerous methods have heretofore been employed in attempts to form sheet materials of a smokeless powder composition for use in the manufacture of combustible cartridge cases, propellant charges, laminated and rollshaped propellants and the like. Among the methods previously used are those wherein preformed cellulosic sheet materials, such as woven fabrics, are saturated with nitroglycerin. In other methods the smokeless powder compositions are colloided with the aid of volatile solvents and rolled or extruded through dies in sheet form. In still other methods nitrocellulose sheet materials are formed by suitably nitrating cotton fabrics, etc. All of these methods, however possess numerous inherent disadvantages. Thus where cotton fabrics are saturated with explosive liquids or are formed into nitrocellulose by nitration of preformed fabrics, little variation is possible in the composition of the final material. Also the finished sheet is, in most cases, difficult to handle due to noticeable lack of and non-uniformity of tensile strength. No really precise control can be maintained over the process and the product itself cannot be tailor-made to fit the exacting requirements of the end use. Thus lack of uniformity in the composition, strength, burning rate and other characteristics of the sheet material result in an end product having undesirable and to some extent unpredictable ballistic properties. In those cases where a colloidal mass of propellant composition is extruded in film or sheet form, greater uniformity of the chemical and physical characteristics of the sheet is possible and thus greater control over the ballistic properties of the final propellant may be achieved. However, such methods, as well as the products resulting therefrom, possess other undesirable characteristics. Thus' uniformity in sheet thickness, width etc., is difficult to achieve due to uneven shrinkage during drying. The periods of drying the sheet are undesirably lengthy and difiicult to control with any degree of accuracy. Even more important, the finished sheets present a solid, unbroken surface and by reason of this lack of porosity little or no control can be attained in varying the burning time of the sheet of a given chemical composition.

The above recited diflioulties encountered in formulating solid propellant compositions in sheet form and having uniform, determinable and reproducible ballistic characteristics serve to emphasize the importance to be accorded the development of an eflicient, rapid and inexpensive method of producing highly combustible sheet materials having ballistic properties of considerable uniformity and subject to precision control by the manufac turer or designer and yet which may at the same time be tailor made to fit the requirements of the particular end use.

Accordingly, a primary object of this invention is the development of a highly combustible sheet material, the burning rate of which is subject to precision control with nited States atent 2 or without the necessity of varying the chemical com position or dimensional characteristics of the sheet.

A further object of the invention is the provision of highly combustible sheet materials composed of solid propellant compositions in the form of textile-type fibrous units.

A still further object of the invention relates to various methods of forming non-woven fabrics, webs, papers and the like, composed at least in part of solid propellant compositions in fibrous form.

Another object is the development of flexible propellant sheet materials having any desired degree of porosity and whose chemical composition is capable of wide variations without loss in mechanical and ballistic properties.

A still further object of the invention is the elimination of the conventional time consuming steps of colloiding, blending and drying necessary in prior art methods of extruding propellant sheet materials.

Other objects and advantages of the invention will become obvious to those skilled in the propellant art as the invention is hereinafter particularly described.

I have now found that the foregoing objects may be accomplished according to one modification of my invention by extruding nitrocellulose propellant compositions through spinnerettes in the form of textile-type continuous filaments, staplizing said continuous filaments by cutting into any desired lengths, and, subsequently forming said staple, propellant fibers into non-woven fabrics, papers and the like by techniques to be described in greater detail below.

As stated in my parent application Serial number 697,296, filed November 18, 1957, and entitled Solid Propellants in Textile Form, of which this application is a continuation-in-part, numerous propellant compositions of the nitrocellulose type, may be formed into a spinning dope by solution in any suitable volatile solvent such as acetone. This spinning dope or lacquer is then extruded under pressure through spinnerettes similar to those normally employed in the manufacture of synthetic textile fibers and solidified into solid, continuous, filaments by either the wet or dry spinning methods conventionally used, for example in the spinning of viscose, cellulose acetate, and like textile filaments. The resulting, textiletype filaments are then cut into staple fibers and formed into matts, non-Woven fabrics, papers and like sheet materials as desired.

In a second modification of the invention fibers of nitrocotton are combined with suitable plasticizers, stabilizers and like ingredient and formed into paper-like sheet materials by techniques which will be explained in greater detail below.

The products and methods of this invention are more clearly illustrated in the accompanying drawings wherein:

FIG. 1 schematically illustrates one form of an apparatus suitable for use in the formation of non-woven fabrics from propellant fibers.

FIG. 2 illustrates a section of a non-woven fabric or web produced by the methods of this invention.

FIG. 3 diagrammatically illustrates a form of apparatus used in the manufacture of propellant papers.

In the practice of this invention, any substantially non-crystalline, propellant composition which is capable of forming a flexible, tenuous textile-type filament on extrusion through .a spinnerette may be employed. In general, however, it has been found that compositions containing large proportions of nitrocellulose are most adaptable to the method and desired end use. In addition to nitrocellulose, such compositions may contain stabilizers, explosive stabilizers, plasticizers, coolants and other modifying agents customarily used in the blending of propellant compositions. The thus formed composition is dissolved in any compatible, volatile solvent such as acetone and extruded under pressure through a spinnerette having a multiplicity of orifices of a size suitable to result in a filament of the desired denier. The filaments may be spun by either the wet or the dry method. In the dry method the filaments leaving the spinnerette pass through a stream of warm, humid air for a distance sufficient to solidify the spinning composition and remove the bulk of the acetone or other solvent. In the wet spinning method, the filaments leaving the spinnerette pass directly into and through an aqueous bath to solidify the filamentary material and remove any solvents present. The aqueous bath may be simply water or a dilute solution of such salts as are customarily employed in coagulating synthetic filaments such as viscose.

During the period of solidification and formation, tension is exerted on the filaments sufficient to. stretch them to effect molecular orientation and thus increase the tensile strength and decrease the diameter of the filaments to any desired size. At this point, the filaments may be given a slight twist just sufficient to hold the bundle together in the form of a unitary strand, and wound on a storage spool for subsequent processing. However, in most cases the filaments will be cut into suitable lengths, as for example, /2 to 2 inches, and either immediately processed into web form or stored for future use. Filaments having any desired denier may be formed by the above method. However, for practical purposes it has been found that filaments having deniers ranging from 3.75 to about 8.0 are to be preferred. Any desired number of filaments may be extruded simultaneously depending on the number of orifices in the spinnerette. For the purposes of the work discussed herein, spinnerettes having 40 and 50 orifices respectively were employed. However, the number of such orifices may run as high as 200 or more.

The staple fibers formed by the above method are blended and formed into a web of interlaced fibers. This web of fibers is then formed into a non-woven fabric by the application of heat and pressure. Where the bulk of the fibers are non-thermoplastic or where the application of heat sufficient to plasticize thermoplastic fibers is considered to be objectionable, it is usually necessary to add a bonding agent to the fibers to obtain a strong, cohesive web. Such a method, and the apparatus eniployed therein, are shown diagrammatically in FIG. 1 wherein the blended, staple fibers are fed through a fiber opener which may be a picker of the type commonly used in textile industry. The fiber mass is then formed into a web by means of a conventional garnetter or an apparatus of the Curlator Rando-Feeder and Rando- Webber type. In cases where a garnetter is employed the fibers are substantially in a parallel arrangement. The web issuing from the garnetter is generally thin and tenuous and should be lapped to form a sheet having a plurality of layers capable of giving a fabric of desired thickness. The Rando-Webber type apparatus is capable of forming a thicker Web wherein the fibers are randomly distributed and hence no lapping operation is necessary. The web is then treated with a solution of a bonding agent by means such as a spray nozzle, an impregnator and the like. Numerous resin or other adhesives which are compatible with the propellant fibers and are capable of being dried and/or cured may be used. Among the bonding agents which are suitable for use are:

Reclaimed rubber Asphalt emulsion Gelatin Casein Polyvinyl acetate Polyvinyl chloride Rubber latex (natural) Rubber latex (synthetic) emulsification are diluted to the desired solids concentration. The ability to vary the concentration and composition of bonding agent solutions and emulsions provides a wide latitude in the range of physical properties of the finished, bonded webs. Thus the strength, flexibility, absorbancy, hand, permeability, wet strength and other properties may be readily varied to meet product requirements. The amount of bonding agent added may vary from \0.5% to 50% based on the fabric weight. Also where the bulk of the fibers are of a thermoplastic nature, the step of adding a bonding agent may be eliminated entirely and the fibers bonded together by the application of heat in an amount sufficient to soften or gelatinize the fiber surfaces and cause them to adhere firmly together. Still another method of bonding is afforded by the use of a fiber solvent such as acetone.

After leaving the bonding agent applicator, the web should pass between -a series of pressure rollers to compress the web to form a nonwoven fabric of desired thickness. The fabric is then passed through a drying oven or other means for drying and/ or curing the bonding agent.

Variations in the above mentioned non-woven fabrics may be made by using fibers of different staple lengths, mixtures of fibers of varying lengths, blends of the propellant fibers having different chemical compositions and variation in the amount of binder and degree of compression of the web. Also, if dilution is desired, varying amounts of a non-propellant fiber such as cotton, cellulose acetate, viscose and the like may be blended with the propellant fibers. The strength of the fabric may also be increased by use of fibers crimped by any conventional textile crimping means either before or after cutting into staple lengths.

For purposes of this invention, regenerated cellulose nitrate fibers are defined as cellulose nitrate fibers artificially formed as the result of processing a solvent solution or dispersion of cellulose nitrate as previously described. Nitro-cotton is defined as cellulose nitrate fibers which have been produced by the nitration of cellulose and subsequently purified without dissolving the fibers in the process.

The following specific examples are given by way of illustrating this modification of the invention.

In these examples as elsewhere throughout the specification and claims, all parts and percentages are given in terms of weight unless specifically designated to the contrary.

Example 1 Continuous, textile-type filaments were spun using the following propellant composition:

Percent Nitrocellulose (12.6% N) Dinitrotoluene 10 Dibutylphthalate 5 Diphenylarnine (added) l A solution of one part of the above composition in four parts of acetone was filtered and extruded under pressure through a spinnerette to form filaments having denier of 3.75 in accordance with the method described in my parent application. The dried, oriented filaments were cut into staple lengths ranging between /2 and 2 inches. The fiber mass was fed into a garnett machine and formed into a thin web of fibers in substantially parallel arrangement. This web was then lapped to form a sheet composed of a plurality of layers of sufiicient total thickness to yield a non-woven fabric of the desired dimensions. A synthetic rubber latex emulsion was sprayed on the lapped blanket of fibers in an amount sufficient to deposit approximately 5 percent solids based on the final weight of the fabric. The fiber blanket was then subjected to a series of compression rollers and dried in an oven as previously described. For safety purposes the operation up to the application of the bonding agent is carried out under conditions of very high humidity and all apparatus is properly grounded. The resulting non-woven fabric exhibited good flexibility and hand and Was well suited for use as propellant charges in either roll or sheet form. For example, the fabric may be formed into a combustible cartridge case by winding a number of layers on a mandrel and bonding the layers together with either a volatile solvent such as acetone, or a non-volatile plasticizer or a resin, with or without the application of heat and pressure. After reaching the desired diameter, the tube is removed from the mandrel and allowed to dry or cure. Another technique for making such products from the non-woven fabrics of this invention is to laminate sheets of the fabric and then cut, or shape them under heat and pressure to any desired form.

Example II Filaments having a denier of 8.0 and the following composition Were formed in accordance with the method described in my parent application:

Percent Nitrocellulose (13.25% N) 79.90 Nitroglycerin 19.50 Ethyl Centralite 0.60

The above filaments were cut into staple lengths of approximately two inches and blended with an equal quantity of staple fibers of the type described in Example I. The blended fibers were run through fiber openers and pickers and fed to a breaker card of a type commonly used in the textile industry to form fiber webs. The resulting cross-webbed laps, the fibers of which are crossed in a diagonal manner was fed between two sections of wire mesh and dipped into a bonding solution of gelatin. Excess binder solution was squeezed out and the fabric oven dried. The final non-woven fabric contained approximately 2% binder by weight. For most purposes the screen conveyor is run at a speed of -12 feet per minute, but if desired may be increased up to as much as 24 ft./min.

In a second basic modification of the invention the propellant sheet material is produced by resin bonding textile-type staple fibers deposited from an aqueous slurry and then drying and/or curing the web under pressure and heat. This method is similar to that used in the manufacture of pulped paper products.

In this modification, either regenerated nitrocellulose fibers or nitro-cotton may be used. Depending on the chemical composition of the fibers, additional plasticizers and/ or bonding agents may be added to the aqueous slurry to obtain a propellant paper of the desired ballistic properties. Briefly, either of the above types of nitrocellulose fibers having the proper length, are slurried in water with a plasticizer such as triacetin or dibutylphthalate and a stabilizer such as diphenylamine, ethyl or methyl centralite and then converted into paper on conventional papermaking machinery. Various plastic or emulsion type rubber latices may be incorporated in the slurry as the binder in the finished paper instead of the plasticizer. As in the case of the non-woven fabric, various water soluble binders such as starch, casein, gelatin, methylcellulose or gums may also be used to obtain desired physical properties in the propellant paper.

FIG. 3 illustrates the simplified operational steps involved in paper making. The first basic step involves the formation of a slurry of the fiber in the water in the beater. This step reduces the fiber length to a desired freeness, the freeness being a measure of the rate at which water will flow through a mat of fibers under a given set of conditions. The fiber slurry from the beater is pumped into the stock chest where chemical additives and binders are usually added under agitation. Additives may also be added to the slurry in the beater if desired. From the stock chest the suspension of fibers is passed onto the Fourdrinier screen where the wet mat is formed.

This mat is carried continuously onto a drier section to remove excess water and apply any desired surface finish to the paper.

Example III A nitrocellulose paper was prepared having the following composition:

Hycar-1551 is a copolymer of butadiene and acrylonitrile, fully identified on page 284 of Handbook of Material Tradenames, published by Industrial Research Service in 1953.

The sulfate woodpulp cellulose was added to a beater /2 /a full of water and beaten to a freeness of 450. The nitrocellulose, in the form of loose nitrated cotton fibers, and the diphenylamine in a methanol solution were added to the heater and the whole thoroughly blended together. The woodpulp-nitrocellulose blend was added to the stock chest of a papermaking machine and Hycar-1551 emulsion was added thereto. The pH of the slurry was adjusted to approximately 8.5 by the addition of a small amount of aqueous ammonia prior to the addition of the Hycar. While under agitation, very small amounts of alum solution were added to precipitate the Hycar onto the fibers. The final pH of the blend was approximately 6.6. The slurry of fibers was then fed from the stock chest to the Fourdrinier screen and a mat formed in the same manner as a paper mat is formed. There was no difliculty running the paper on the Fourdrinier machine and drying sections. The optimum rate of speed for this batch was 38 ft./min. The moisture content of the finished paper was between 30 and 35%. The thickness of the uncalendered paper was 27 mils while the thickness of the calendered paper was 19 mils. A small amount of silicone or other antifoam compositions may be added to the slurry in the beater to prevent foaming and aid in the formation of a homogeneous slurry.

Example IV A second batch of propellant paper was prepared using regenerated nitrocellulose propellant filaments having the composition given in Example I. The filaments were cut into lengths of A inch or less and slurried in a beater with sulfate woodpulp cellulose fibers to a freeness of 450. Approximately 15% woodpulp based on the weight of the propellant fibers was used.

To the slurry was added 1% guar gum based on the total weight of fiber present. This mixture was slurried for ten minutes and then pumped to the chest. The pH of the slurry at this point was 7.3. With the agitator going in the chest, a small amount of aqua ammonia was added to raise the pH to approximately 8.8. At this point Hycar-1551 emulsion in the amount of 1% solids based on the weight of the total fiber present was added and agitation continued for an additional 10 minutes. An aqueous alum solution was added in very small amounts to lower the pH and thereby break the Hycar emulsion and deposit the latter on the cellulose fibers. The final pH of the slurry was 6.6.

The total mix now had a freeness of 650. This was dropped on the Fourdrinier screen the speed of which was 38 ft./min. The mat carried well from the screen to the drying section of the papermaking machine.

Any desired amount of woodpulp cellulose fibers may be blended with the propellant fibers depending on the ballistic properties and strength of the paper web desired. When amounts of woodpulp cellulose less than about 5% by weight based on the dry weight of the propellant fibers are used however, the fiber web has insufficient strength to pass freely from the Fourdrinier screen to the drier belt and drying sections of the papermaking machine. In

directly into the paper itself.

It is to "be emphasized that-the physical characteristics and chemical compositions of either the nonwoven fabric or paper modification of this invention are subject to wide variation, thus affording a means of attaining precision control over the burning rate and other ballistic properties of :the final propellant sheet material. Thus the denier of the regenerate cellulose filaments may be varied at will, the preferred range being from 3.75 to about 8.0 but actually beinglimited only by mechanical difficulties in handling extremely fine or very coarse filaments. Various staple length fibers may be employed, or blends of a variety of lengths. The chemical composition may be varied to include filaments spun from any nitrocellulose type propellant either of the single or double base type. Thus the explosive ingredient may consist solely of nitrocellulose, or a varying amount of the nitrocellulose may be replaced by nitroglycerin, dinitrotoluene or the like. Nitrocellulose of any degree of nitration may be employed. However, nitrocellulose having a nitrogen content of from 12.6 to 13.25 percent has been found to be most satisfactory. Nitrocellulose compositions having a high crystalline content are in general unsatisfactory and for all practical purposes a crystalline content greater than about 20% has been found to form filaments too fragile to be used in the manner intended.

For the purposes of this invention and disclosure, terms such as textile-type filamentary material and the like are defined as including any materials composed of, or containing structural units having dimensions, strength, flexibility and other characteristics sufficiently similar to conventional textile fibers to permit their processing on conventional textile machinery to form textile-type strands, fabrics and the like. By terms such as textiletype fibers, staple length fibers and the like is meant fibrous material having physical properties similar to those of conventional textile staple fibers but of a length which may vary from less than a quarter of an inch when used to form sheets by papermaking methods, up to a length of several inches when used in the manufacture of non-woven fabrics.

From the above'detailed disclosure and examples it will be apparent to those skilled in the art, that I have now discovered new and novel forms of sheet propellant material ideally suited for use in the manufacture of highly combustible products such as solid propellants, igniter tubes, cartridge cases, sporting goods cartridges, commercial explosives and the like. The new propellant form is capable of adaptation to an almost infinite variety of forms, shapes and ballistic properties by variation of fiber denier and length, chemical composition, and the porosity of the sheet material as well as other variables which will be apparent to those skilled in the art. This novel form of propellant presents numerous advantages over previously known forms, for example, precision control over the ballisticproperties of the web; its use as a propellant charge withoutthe aid of conventional cartridgecases and like containers; it affords an increased density of loading of propellant over conventionalgranular-artillery propellant; it offers greater flexibility and mechanical'strength particularly at lowtemperatures; blending of the propellant is not necessary, and it is possible to obtain improved chemical uniformity over that of conventional propellants. Furthermore the methods employed-inmanufacturing the novel propellant forms, eliminates the present colloiding processes as well as the usual lengthly drying cycles. Manufacture of the propellant webs, fabrics and papers may be accomplished on standard textile or paper making equipment.

In the foregoing description I have disclosed preferred embodiments of my invention. However, it is not intended that this invention be limited to the specific examples set forth above, as it will be apparent to those skilled in the art, that the chemical composition and physical characteristics may be varied over a wide range without departing from the spirit of the invention or exceeding the scope of the appended claims.

Having thus described the invention, what is claimed as new is:

1. Highly combustible, fibrous material composed essentially of a spun nitrocellulose propellant composition in the form of uniform synthetic filaments, said propellant composition consisting essentially of approximately 99 percent nitrocellulose having a nitrogen content of from 12.6 percent to 13.25 percent and approximately 1 percent diphenylamine.

2. Highly combustible, fibrous sheet material composed essentially of a spun nitrocellulose propellant composition in the form of uniform synthetic filaments, said propellant composition consisting essentially of approximately 85 percent'nitrocellulose having a nitrogen content of from 12.6 to 13.25 percent, 9 percent dinitrotoluene, 5 percent dibutylphthalate and 1 percent diphenylamine.

3. Highly combustible, fibrous sheet material composed essentially of a spun nitrocellulose propellant composition in the-form of uniform synthetic filaments, said propellant composition consisting essentially of approximately 79.9% nitrocellulose having a nitrogen content of at least 12.6 percent, approximately 19.5 percent nitroglycerin and about 0.6% ethyl centralite.

4. A method of making a web of nitrocellulose material which comprises admixing 85 percent by weight of nitrocellulose, 10 percent by weight of dinitrotoluene and a plasticizer for the nitrocellulose and a stabilizer for the nitrocellulose selected from the group consisting of diphenylamine, ethyl and methyl centralite, with a solvent for said nitrocellulose to form a solution, spinning said solution into filaments, cutting the resulting filaments to a length of from about one-half to two inches and forming a web from the cut filaments.

5. A method of making a web of nitrocellulose material which comprises admixing 79.9 percent by weight of nitrocellulose, 19.5 percent by weight of nitroglycerin and a stabilizer for the nitrocellulose selected from the group consisting of diphenylamine, ethyl and methyl centralite, with a solvent for said nitrocellulose to form a solution, spinning said solution into filaments, cutting the resulting filaments to a length of less than about a quarter inch and forming a web from the cut filaments.

References Cited in the file of this patent UNITED STATES PATENTS 1,028,748 Lederer June 4, 1912 1,896,642 ONeil Feb. 7, 1933 2,091,969 Dreyfus Sept. 7, 1937 2,320,243 Mackey "a May 25, 1943 2,401,236 Fielitz May 28, 1946 2,514,412 Owens July 11, 1950 FOREIGN PATENTS 300,668 Germany Sept. 21, 1920 

1. HIGHLY COMBUSTIBLE, FIBROUS MATERIAL COMPOSED ESSENTIALLY OF A SPUN NITROCELLULOSE PROPELLANT COMPOSITION IN THE FORM OF UNIFORM SYNTHETIC FILAMENTS, SAID PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF APPROXIMATELY 99 PERCENT NITROCELLULOSE HAVING A NITROGEN CONTENT OF FROM 12.6 PERCENT TO 13.25 PERCENT AND APPROXIMATE1 PERCENT DIPHENYLAMINE. 